Hole effective masses in relaxed Si1-xCx and Si1-yGey alloys

We report hole effective mass calculations of Si1-xCx and Si1-yGey alloys. All calculations are based on a 16 x 16 Hamiltonian matrix constructed from the linear combination of atomic orbital approximation with spin-orbit interaction taken into consideration. The 1 meV constant energy surfaces below the valence band edge are used to determine the nominal hole effective masses, The effective masses of light hole and heavy hole of Si1-yGey alloys vary as linear functions of Ge content and increase linearly as the hole energy increases from 1 to 15 meV. The heavy hole effective masses of Si1-xCx alloys, however, exhibit a totally different trend, The effective mass of Si1-xCx remains relatively unchanged from x = 0.0 to x = 0.9, and increases abruptly by a factor of two from x = 0.9 to x = 1.0. The nonparabolicity increases as the C content rises up to x = 0.9, and nearly disappears when turning into pure diamond. The interaction between the split-off hole band and the heavy hole band is proposed for the anomalous behavior of the heavy hole effective masses of SiC alloys. (C) 1997 American Institute of Physics.